1. Field of the Invention
The present invention is related to a fiber sensors which have a preferred, useful, rotational orientation, and to a method for easily identifying that orientation to a user of the sensor. In particular, the present invention is drawn to an optical fiber sensor having an asymmetric feature or xe2x80x9csensingxe2x80x9d means, which is intended to be fixed to a mechanical structure for remotely sensing a physical parameter, and to a method for adapting the fiber to such a use.
This invention also relates to a means for deploying a sensing system, and more particularly to a sensing system utilizing an asymmetric optical fiber, which enables the continuous non-destructive monitoring of a component in more-or-less real time.
2. Prior Art
There is increasing interest and use of composite materials, for many years. Typically, such composite materials comprise various layers or plys of a fiber, e.g. glass fiber, carbon fiber, or some other fiber, bonded together by a resin or polymer.
For various reasons, composite materials are gaining wide acceptance in many industries where the ability to accurately monitor component structural integrity or surrounding environmental conditions is vital. Furthermore, with the development of fibers having embedded anisotropic mechanical features it is now possible to monitor several physical parameters simultaneously. See U.S. Pat. Ser. Nos. 5,828,059 and 5,591,965.
Monitoring techniques have been proposed, using a network of optical fibers embedded into the structure of a component and forming an integral part of it, and such techniques potentially have a number of advantages. Theoretically, through the use of optical fiber sensing technology can be used for a number of purposes: e.g. impact detection and location; delamination and microcrack detection and location; strain and deformation mapping.
It is known to embed optical fibers into a composite material. One proposal can be found in U.S. Pat. No. 4,581,527 (Crane et al) disclosing a damage assessment system using a three-dimensional grid of embedded optical fibers. U.S. Pat. Nos. 4,854,706, 5,210,499 and 5,367,376 discuss embedding optical fibers in resins or resin impregnated tapes. Furthermore, U.S. Pat. Ser. No. 4,854,706 discusses orienting the optical fiber within the resin composite. However, none of the references have been found to teach a means for attaching an orientation marker or xe2x80x9cflagxe2x80x9d onto the fiber shank in order to permit the quick identification of the fiber orientation at a later time subsequent to application of the flag.
It is therefore an object of this invention to provide a means for identifying the position of a sensor which yields an asymmetric response to an input load.
A object of this invention is to provide a means for identifying the angular position of one of a radial axis of an optical fiber having a sensor exhibiting an asymmetric load response.
Yet another object of this invention is to provide a tag or xe2x80x9cflagxe2x80x9d attached to the exterior of the optical fiber or sensor such that the axis of interest lies either in the plane of the xe2x80x9cflag,xe2x80x9d perpendicular to it, or at some known rotational orientation.
Still another object of this invention is to provide an optical fiber having a sensor exhibiting an asymmetric load response embedded in a prepreg tow.
Another object of this invention is to provide a method for embedding a fiber within a composite media such that anisotropic mechanical strain may be detected by an embedded fiber having a sensor exhibiting an asymmetric load response.
Yet another object of this invention is to provide a method for embedding a fiber within a prepreg tow such that resin is prevented from xe2x80x9cpoolingxe2x80x9d or forming preferentially zones or pockets at the surface of the fiber, especially along a seam between a sandwich of tow of said prepreg tows.
Additional objects and advantages of this invention will become apparent to those skilled in these arts as the following specification and claims is reviewed.